The natural range of sea level for the past 3 million years is from a high of 35 meters above present sea level, to a low of 120 meters below present sea level:
The +35 m value is from the warm period that occurred during the mid-Pliocene, before the Earth plunged into the Quaternary cycle of alternating ice ages and interglacial periods (we live in an interglacial). In the mid-Pliocene, lowlands such as much of Florida and the lower Mississippi River valley were under water.
The -120 m value is from peak-glacial times, when large quantities of water were stored on the continents in continental ice sheets which were over 1000 meters thick covering millions of square kilometers. In this time, large areas of continental shelf were exposed, such as a wide area west of the current Florida coast, and the Bering Land Bridge that linked Alaska and Siberia.
The slight changes in sea level that have been observed during the past century (2-3 mm per year) are largely due to the expansion of sea water as global temperatures have increased. The wide range of sea level over the past three million years is mostly due to changes in the amount of water stored on the continents as ice. Because of the high density of human settlement and development along coastlines, even modest changes in sea level, on the order of 0.5 to 1.0 meters, could cause havoc in low-lying areas.
The geological perspective is: change is the norm in the Quaternary.
Grace and peace